This project will refine a previously developed psychophysiological assessment procedure for use with VietNam veterans suffering from Post Traumatic Stress Disorder (PTSD) and concomitantly produce information related to the possible etiology of PTSD. VietNam veterans suffering from PTSD will be compared to age and sex matched subjects from the following groups: (1) VietNam veterans who do not meet the criteria for PTSD; (2) VietNam-Era veterans who did not serve in VietNam; (3) non-veterans; and (4) individuals suffering from a different anxiety disorder as defined by DSM-111. A comprehensive assessment will be conducted involving: (1) psychological and affective states as measured by standard psychological tests and structured interview; (2) psychophysiological responses (heart rate, blood pressure, skin temperature, skin resistance and forehead muscle tension level) measured during rest and mental arithmetic and while the subject listens to an audio tape of combat sounds played at progressively louder sound levels; (3) behavioral avoidance assessed by how long the participant can listen to the combat sounds audiotape. Relations between all three measures and combat experience will also be examined.